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08-26-2004 06:55 AM
08-26-2004 06:55 AM
VGSPLIT - Split LVOLS to Different VG
With VxVM, we can split a Volume's mirror-plex (up to 32 allowed). Then move the disks/luns comprising those mirror plex to another Diskgroup (which could be on another server) and rebuild the DiskGroup, the volumes and mount.
Is there a similar thing in LVM? Or do I need to have Cluster LVM for this purpose?
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08-26-2004 07:04 AM
08-26-2004 07:04 AM
Re: VGSPLIT - Split LVOLS to Different VG
Based on this, I don't think it would be possible to move a particular PV with a split mirror to a different VG. I think that would go against HP's intended use of splitting mirrors.
I think the main intention is to split a mirror, mount a backup the split copy, and then merge the mirrors back. The merge task would be quite difficult, if not impossible, if the split mirror were in a different VG.
Patrick
P.S. Do you have your new Harley yet? :)
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08-26-2004 07:08 AM
08-26-2004 07:08 AM
Re: VGSPLIT - Split LVOLS to Different VG
This is how you can do it
1) Mirror the Logical volumes. Here is the trick. The allocation policy for ther logical volumes should be PV strict or PVG-strict. Otherwise, you dont have control over which PV the logical volume will be mirrored to.
It would be a good idea to define all the primary PVs in one PVG, the mirror PVs (that are going to be taken out) as another PVG and mention the allocation policy for the LV as PVG-Strict.
2) Split the LVs. This will create the logical volume device files in the system. By default "b" is appended to the logical volume device file.
3) Deactivate the volume group.
4) Export the volume group and re-import with only the primary PVs.
5) If you are going to mount in the same node, then you need to execute vgchgid commands on the mirror PVs. This is because these mirror PVs will have the same VGID as the primary PVs and the kernel will not allow more then one VG with the Same VGID
be activated.
If you are going to mount the mirror PVs in a different node, then this step is not required.
6) Once vgchgid is successful, Create a new volume group directory, group file and vgimport with the mirror PVs.
7) fsck the file system and mount them.
Hope this helps
-- Sundar.
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08-26-2004 07:11 AM
08-26-2004 07:11 AM
Re: VGSPLIT - Split LVOLS to Different VG
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08-26-2004 07:11 AM
08-26-2004 07:11 AM
Re: VGSPLIT - Split LVOLS to Different VG
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08-26-2004 07:13 AM
08-26-2004 07:13 AM
Re: VGSPLIT - Split LVOLS to Different VG
I cannot think of any other way of doing this.
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08-26-2004 07:36 AM
08-26-2004 07:36 AM
Re: VGSPLIT - Split LVOLS to Different VG
The split LUNs containing the mirror LVOLS will need to be on a different VG on a different server (we use LUN multi-hosting/pathing btw..)
And there can never be downtime on the Main/Primary Volume Group...
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08-26-2004 07:39 AM
08-26-2004 07:39 AM
Re: VGSPLIT - Split LVOLS to Different VG
Since you mention LUNs I assume you are on a disk array of some sort? If so, what kind? Does it have the capability to do BCV's (Business Copy Volumes) or something similar? If you can do BCV's then you could create a business copy on another LUN and then mount that on a different server. Since BCV's are created at the disk array level, LVM never enters the picture, hence you can take a BCV lun and mount it on another system.
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08-26-2004 07:47 AM
08-26-2004 07:47 AM
Re: VGSPLIT - Split LVOLS to Different VG
Well we actually use Business Copy on the EVA's but it's been plagued with problems and cannot mirror to a different EVA. Besides, the "levelling" processes during the snapclone and the undo process can be quite taxing on the EVA.
That is why we're looking at host based (software) solutions like VxVM. VxVM's mirroring which is multi-treaded btw, (plus FlashSnap) only has a minor effect if done right. Since we only need weekly refreshes of our large Oracle instances, it does not matter if the synch-up/mirroring happen over a span of several days -- as long as on saturday we get "several" copies of our production environments. VxVM allows up to 32 mirrors. And we're already doing this on our Solaris environments albeit using a moer powerful array than the EVA...
BTW, I have'nt got the Harley yet... am still in the process of gettin my License.
Can send pictures once I get it...
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08-26-2004 08:19 AM
08-26-2004 08:19 AM
Re: VGSPLIT - Split LVOLS to Different VG
We can try a crude method here. But not sure if this is going to work.
1) Split the mirrors
2) Have a copy of the LVM configuration file./etc/lvmconf/vgXX.conf
3) vgreduce the PVs
4) vgcfgrestore using the "saved" lvmconf file to the PVs that contain the mirror copy
5) Import them in the another node as a VG
6) fsck and mount the lvs.
As I said, not sure if this is going to work. :-)
-- Sundar
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08-26-2004 09:23 AM
08-26-2004 09:23 AM
Re: VGSPLIT - Split LVOLS to Different VG
Only VxVM is the viable solution in this case .. we cannot do it on hardware - EVA Business Copy unless Contiou$ Acce$$ $oftware is purcha$ed. Problem is we're running these operations on rp8420's and SuperDOmes where Full VxVM licenses and maintenance are expensive...
I'll see what management says... as we are already using this approach on HDS (XP Storage) and Solaris 8/9 VxVM.
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08-26-2004 09:34 AM
08-26-2004 09:34 AM
Re: VGSPLIT - Split LVOLS to Different VG
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08-26-2004 11:16 AM
08-26-2004 11:16 AM
Re: VGSPLIT - Split LVOLS to Different VG
This may not be the cleanest method, but the best I could come up with.
1) Mirror the Logical volumes. Here is the trick. The allocation policy for ther logical volumes should be PV strict or PVG-strict. Otherwise, you dont have control over which PV the logical volume will be mirrored to.
It would be a good idea to define all the primary PVs in one PVG, the mirror PVs (that are going to be taken out) as another PVG and mention the allocation policy for the LV as PVG-Strict.
2) Split the LVs. This will create the logical volume device files in the system. By default "b" is appended to the logical volume device file.
Here is the catch
3) After splitting the mirror, you need NOT deactivate the volume group and export the vg IF the mirror copies are to be mounted on a different server
On the target server
a) Create the VG dir, group file
b) Import the VG with only Mirror PVs. These PVs are already part of the VG in the Source system. But that doesnt matter.
c) FSCK and mount the logical volumes.
4) Once you are done with the copies (like backup etc), do a vgchange -a y on the source system and execute lvmerge.
This way there is no downtime involved.
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08-26-2004 06:58 PM
08-26-2004 06:58 PM
Re: VGSPLIT - Split LVOLS to Different VG
VxVM looks like your best and only real option in this scenario.
HTH
Duncan
I am an HPE Employee

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08-26-2004 08:15 PM
08-26-2004 08:15 PM
Re: VGSPLIT - Split LVOLS to Different VG
After making the splitted mirror, you activate the volume group on all other nodes in read-only mode and then copy the data from the splitted lvol to a read-write lvol to use it.
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08-30-2004 12:14 AM
08-30-2004 12:14 AM
Re: VGSPLIT - Split LVOLS to Different VG
Thanks all.